Primary transfer for simplex mode forward-link high-speed packet data services in CDMA systems

ABSTRACT

A back haul architecture enables efficient primary transfer (i.e., transfer of the designation of primary base station from one base station to another). A frame selection/distribution (FSD) function queues packets of forward-link data—to which sequence numbers have been assigned—for packet-mode transmission over the back haul only to one base station—the current primary base station—where the packets are again queued for over-the-air transmission to the mobile unit. If and when it becomes appropriate to transfer the designation of primary base station to another base station, there may still be packets of data queued at the old primary base station awaiting transmission to the mobile unit. The old primary base station sends a message to the new primary base station indicating a particular sequence number that identifies the remaining packets of forward-link data queued at the old primary base station. The new primary base station then sends a message to the FSD function requesting transmission of those packets of forward-link data corresponding to the particular sequence number. The FSD function then transmits those requested packets of forward-link data to the new primary base station, which queues the requested packets for over-the-air transmission to the mobile unit. In this way, transmission of all of the forward-link data to the mobile unit is enabled without having to transmit the remaining queued packets of forward-link data from the old primary base station to the new primary base station over the back haul, thereby providing an efficient mechanism for primary transfer in wireless communications systems that support forward-link data transmissions only in simplex mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is one of a set of U.S. patent applications consistingof Ser. No. 09/330,888, Ser. No. 09/330,582, and Ser. No. 09/330,509,allof which were filed on the same date and the teachings of all of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to telecommunications, and, in particular,to wireless communications systems conforming to a code-division,multiple-access (CDMA) standard, such as the cdma2000 standard of theIS-95 family of CDMA wireless standards.

2. Description of the Related Art

FIG. 1 shows a block diagram of a conventional CDMA wirelesscommunications system 100. Communications system 100 is assumed toconform to the cdma2000 standard in the IS-95 family of CDMA wirelessstandards, although the present invention is not necessarily so limited.Communications system 100 comprises an interworking function (IWF) 102connected to a radio link protocol (RLP) function 104, which is in turnconnected to a frame selection/distribution (FSD) function 106, which isin turn connected to one or more base stations 110 via back haulfacilities 108 (e.g., T1 lines). Depending on the specificimplementation, IWF function 102, RLP function 104, and FSD function 106may be, but need not be, physically separate functions.

Each base station 110 is capable of simultaneously supporting wirelesscommunications with one or more mobile units 112. FSD function 106performs a forward-link frame distribution function in which frames ofdata corresponding to user messages are distributed to the various basestations. In addition, FSD function 106 performs a reverse-link frameselection function in which frames of data received from the variousbase stations are processed for forwarding on to RLP function 104. Inthe forward-link direction, RLP function 104 segments user messagesreceived from IWF function 102 into frames of data for distribution byFSD function 106. In the reverse-link direction, RLP function 104reassembles packets of data received from FSD function 106 into usermessages for forwarding on to IWF function 102. IWF function 102implements a high-level point-to-point protocol (PPP) to perform certaincentralized functions for communications system 100 to coordinate andcontrol operations at the various base stations 110. IWF function 102also functions as the interface between communications system 100 andother communications systems (not shown) to provide a full range oftelecommunications services to the mobile units, including voicecommunications with a remote end unit and/or data communications with acomputer server or other nodes of a computer network.

As used in this specification, the term “mobile unit” as well as itssynonyms “mobile user,” “mobile,” and “user,” will all be understood torefer to any end node communicating via wireless transmissions with oneor more base stations of a wireless communications system, whether thatend node is actually mobile or stationary. Also, as used in thisspecification, the term “base station” is synonymous with the terms“call leg” (or “leg” for short) and “cell site” (or “cell” for short).

The cdma2000 standard supports different modes of data communications.For relatively low rates of data messaging, a fundamental channel (FCH)can handle both signaling and data messaging. Signaling refers to thecommunications between a mobile and a base station that are used by themobile and the base station to control the communications links betweenthem, while messaging refers to the information passed through the basestation to and from the end nodes of those communications, where themobile is one of those end nodes. For high-rate data messaging, asupplemental channel (SCH) can be used for data messaging, while thefundamental channel handles the signaling between the mobile and thebase station. Alternatively, when an SCH is used for data messaging, thesignaling between the mobile and the base station can be handled by aspecial communications channel called a dedicated control channel(DCCH), which requires less power to transmit than an FCH, which isdesigned to handle low-rate data messaging in addition to signaling.

FIG. 2 shows a functional block diagram of a portion of communicationssystem 100 of FIG. 1 for a mobile unit 112 operating in soft handoffwith three base stations 110. Soft handoff refers to a situation inwhich a mobile unit is simultaneously communicating with two or morebase stations, each of which is referred to as a call leg of thosecommunications. Frame selection/distribution function 106 supports thesoft handoff communications between mobile unit 112 and the three basestations 110.

During normal voice communications, mobile 112 transmits voice messagesusing a reverse-link fundamental channel. Each of the three basestations 110 in soft handoff with mobile 112 receives the reverse-linkFCH, accumulates voice messages into reverse-link packets, and transmitsthe reverse-link packets over back haul 108 to FSD function 106. FSDfunction 106 receives the reverse-link packets from all three basestations, identifies sets of corresponding reverse-link packets (onereverse-link packet from each base station corresponding to the samevoice messages received from the mobile), and selects one reverse-linkpacket from each set of corresponding reverse-link packets to transmitto the rest of the wireless system for eventual transmission to theremote end of the call (e.g., a connection with a regular PSTN user orpossibly another mobile unit in communications system 100).

At the same time, FSD function 106 receives forward-link packetscontaining voice messages from the remote end of the call intended formobile unit 112. FSD function 106 distributes copies of eachforward-link packet to all of the base stations currently in softhandoff with the mobile. Each base station transmits the forward-linkpackets to mobile unit 112 using a different forward-link fundamentalchannel. Mobile unit 112 receives all three forward-link FCHs andcombines corresponding voice messages from all three forward-link FCHsto generate the audio for the person using mobile unit 112.

The timing of the distribution of the copies of the forward-link packetsfrom FSD function 106 to the three base stations is critical, becausemobile unit 112 needs to receive each set of corresponding voicemessages from all three forward-link signals within a relatively shortperiod of time in order to be able to combine all of the correspondingvoice messages together. Similarly, FSD function 106 needs to receiveall of the corresponding reverse-link packets from the different basestations within a relatively short period of time in order to coordinatethe selection of packets for further processing.

In order to satisfy these forward-link and reverse-link timingrequirements, whenever a new call leg is added at a base station (i.e.,whenever a new base station begins communications with a particularmobile unit in soft handoff), special synchronization procedures areperformed between the base station and FSD function 106, e.g., in orderto ensure proper synchronization of that base station's forward-linktransmissions with the forward-link transmissions from the other basestations currently participating in soft handoff with the mobile. Thesesynchronization procedures involve specific communications back andforth between the base station and the FSD function over the back haul.

Although a fundamental channel can support some modest amount of datamessaging in addition to voice messaging, the cdma2000 standard alsosupports high-speed data messaging via supplemental channels. Accordingto the cdma2000 standard, since data messaging is typically bursty(i.e., intermittent), as opposed to the continuousness of voicemessaging, supplemental channels are established and maintained only forthe duration of each data burst. During a burst of data messaging via anassigned SCH, the mobile unit is said to be in an active state. Betweenbursts of data messaging when no SCH is currently assigned, but when anFCH (or DCCH) is assigned, the mobile unit is said to be in a controlhold state. When no dedicated air interface channels are assigned, themobile unit is said to be in a suspended state.

Analogous to the use of a fundamental channel for voice and/or low-speeddata messaging, high-speed reverse-link data messages are transmitted bymobile unit 112 using a reverse-link supplemental channel. Each basestation currently operating in soft handoff with the mobile unitreceives the reverse-link SCH and generates reverse-link packets of datamessages for transmission to FSD function 106 via the back haul. FSDfunction 106 receives the reverse-link packets from all of the basestations and selects appropriate reverse-link packets for transmissionto the remote end of the call (which, in the case of data messaging, maybe a computer server).

Similarly, FSD function 106 receives forward-link packets of datamessages intended for mobile unit 112 and coordinates the distributionof those forward-link packets via the back haul to the appropriate basestations for coordinated transmission to the mobile via assignedforward-link supplemental channels. In addition to the synchronizationprocessing between each base station and FSD function 106 required tomeet the timing requirements for receiving messages at the mobile, indata communications, the base stations need to coordinate theiroperations to ensure that they all transmit their forward-link SCHs tothe mobile at the same data rate. This requires the base stations tocommunicate with one another via the back haul whenever a new burst offorward-link data is to be transmitted to the mobile unit requiring newSCHs to be assigned.

The reactivation time is the time that it takes to change the status ofa mobile unit from either the suspended state or the control hold stateto the active state in which a high-data-rate air interface channel isassigned. In the suspended state, no dedicated air interface channel isassigned to the mobile unit. In the control hold state, the mobile unitis assigned only a dedicated power control and signaling channel. Inprior-art IS-95 CDMA systems, the reactivation time includes the timerequired to assign a new channel to the mobile and the time required tosynchronize each base station with the frame selection/distributionfunction. When the new channel is a supplemental channel to be used fordata transmission to a mobile unit in soft handoff, the reactivationtime also includes the time required for the different base stations tocoordinate their forward-link transmission data rates. In general, thelonger the reactivation time, the lower the data throughput of thewireless system. As such, it is desired to keep reactivation time as lowas practicable.

The back-end architecture, also referred to as the back haul, forprior-art IS-95 CDMA wireless systems is based on providing voiceservice in a wireless environment that supports soft handoff (SHO) onboth forward and reverse links. Voice service is implemented using avocoding function that is provided, for example, in the centralizedlocation of the mobile switching center (MSC), and these resources needto be assigned and freed as calls are set up and cleared. The prior-artvoice-oriented back haul is also used to provide circuit-switched dataservice and has also been applied to packet data service. The rationalefor using the existing voice-oriented back haul for packet data serviceis to save on development cost and time, because much of the existingstructure and operation can be reused. The penalty, though, is to forcelarger-than-necessary delays on the packet service because of the manyset up, clearing, and synchronization operations that are carriedthrough to the packet service, which result in large reactivation timesduring packet data service.

Problems With Using Existing Back Haul Architectures for Packet DataService

The following problems occur when the existing circuit-orientedtechniques for back haul transport are used to support packet data,rather than the voice and circuit-mode data applications they aredesigned to handle.

1. When a mobile call is initially set up, a frameselection/distribution function is chosen by the wireless systemsoftware to service the call, and an initialization and synchronizationprocedure occurs between the FSD function and the base station servingthe call. The synchronization procedure involves exchanging null (noinformation) packets between the FSD function and the (primary) cell fora number of 20-millisecond intervals, until synchronization is achieved.Timing adjustment messages may need to be exchanged between the primarycell and the FSD function before synchronization can be achieved.

These procedures add unnecessary delay when applied to a packet datacall. Packet data calls are generally more tolerant to transmissiondelays than are voice or circuit-mode data calls. If thecircuit-oriented initialization procedure is applied to a packet datacall, an extra delay is added to the time it would otherwise take tobring the user from a suspended state, in which no air interfacechannels are assigned to the user, to an active state, in which at leastone air interface channel is assigned, and the mobile user can beginsending user messages to the FSD function.

2. When secondary legs are added to a call, interactions between thesecondary cells and the FSD function need to occur before user messagescan be transferred from a secondary leg to the FSD function. Hence,these circuit-oriented procedures on the back haul add delay when legsare added to a call.

3. FSD function transmissions to the cell are synchronized to the20-millisecond boundaries of the air interface transmissions. Thisarrangement, among other things, avoids contention and delay at thecells, and saves on the memory that would otherwise be needed to bufferuser messages before their transmission over the air interface. Usermessages arrive at the cell at just about the time they need to betransmitted over the air interface. Such synchronization is required forvoice calls, but might not be required for data calls, unless theforward link of the data call has multiple call legs, in which case,synchronization is required, since all legs must transmit a given usermessage over the air interface at precisely the same time instant. Also,like all circuit-oriented procedures, when used to transport packet datahaving bursty arrival statistics, back haul bandwidth is wasted.

4. The radio link protocol as currently defined in standards (e.g.,Interim Standard IS-707) performs the function of ensuring reliableexchange of user messages between the network and the mobile unit. Ithas provisions to retransmit data received in error, or data missed bythe receiver, and also to discard duplicate received messages. Prior artfor this protocol is to have the network-based end of the RLP functioncoordinate its transmission of information to the base station with therate and format used to transmit user messages over the air. Forcircuit-mode data, this arrangement works well, because the rate andformat are determined when the call is established, and do not changeduring the call. However, for a high data rate packet mode data service,the scarce air interface resource is assigned only when there is data toexchange with the mobile user. The air interface channels are allocatedand de-allocated as needed by the various packet data users. Hence,prior art demands that the network-based RLP function coordinate itstransmission of data with the base stations prior to sending data to thebase stations. This coordination means that delay is added between thetime user data arrives at the RLP function and the time the data is sentto the base stations for transmission over the air to the user.Furthermore, if a packet data user is inactive for a relatively longperiod of time (a parameter fixed by each vendor, but could be on theorder of 30 seconds), prior art would have the RLP functionalitydisconnect from the mobile user. Hence, when data again needs to beexchanged with the mobile user, an additional time delay is incurred tore-initialize the mobile unit with the RLP function.

These enumerated problems point out that applying the circuit mode backhaul procedures of the prior art to a high-speed packet data (HSPD)service causes substantial delays to the high-speed packet data service.It is therefore desirable to design a back haul architecture that (a) isoptimized for packet data service and (b) minimizes the reactivationtime of users due to back haul procedures.

Power Control

According to the cdma2000 standard, each base station 110 monitors thereceive power level of the reverse-link channel signals transmitted bymobile unit 112. Each different forward-link FCH (or forward-link DCCH)transmitted from each base station to the mobile contains a periodicallyrepeated power control (PC) bit that indicates whether that base stationbelieves the mobile should increase or decrease the transmit power levelof its reverse-link channel signals. If the current PC bits in aforward-link FCH indicate that the mobile should decrease its transmitpower level, the mobile will decrease its transmit power level, even ifthe current PC bits in all of the other forward-link FCHs from the otherlegs of the soft handoff indicate that the mobile should increase itspower level. Only when the current PC bits in the forward-link FCHs fromall of the legs indicate that the mobile should increase its transmitpower level will the mobile do so. This power control technique enablesthe mobile to transmit at a minimal acceptable power level in order tomaintain communications while efficiently using the possibly limitedpower available at the mobile and reducing the possibility ofinterference at the base stations with reverse-link signals transmittedfrom other mobile units.

FIG. 3 shows a mobile unit 302 in soft handoff with two base stations304 during conventional reverse-link data transmissions from the mobileunit. According to the prior-art IS-95, standards, a symmetric activeset must be maintained by the forward and reverse links. In other words,the set of base stations currently participating in soft handoff with aparticular mobile unit in the forward-link direction must be identicalto the set of base stations currently participating in soft handoff withthat same mobile unit in the reverse-link direction.

The soft handoff situation shown in FIG. 3 satisfies this requirement.In particular, in the forward link, each base station 304 simultaneouslytransmits in the forward-link direction using either a forward dedicatedcontrol channel (F-DCCH) or a forward fundamental channel (F-FCH). Atthe same time, mobile unit 302 transmits in the reverse-link directionusing a reverse DCCH, a reverse FCH, and/or a reverse supplementalchannel, and those reverse-link signals are simultaneously received andprocessed in parallel at both base stations. Thus, the active set forthe forward link (i.e., base stations A and B) is identical to theactive set for the reverse link. During the active state, each basestation generates power control bits constituting a power controlsub-channel that is multiplexed (i.e., punctured) either on thecorresponding F-DCCH or on the corresponding F-FCH, depending on whichchannel is present.

SUMMARY OF THE INVENTION

The present invention is directed to a back haul architecture thatenables efficient primary transfer (i.e., transfer of the designation ofprimary base station from one base station to another). According to thepresent invention, a frame selection/distribution (FSD) function queuespackets of forward-link data—to which sequence numbers have beenassigned—for packet-mode transmission over the back haul only to onebase station—the current primary base station—where the packets areagain queued for over-the-air transmission to the mobile unit. If andwhen it becomes appropriate to transfer the designation of primary basestation to another base station, there may still be packets of dataqueued at the old primary base station awaiting transmission to themobile unit. According to the present invention, the old primary basestation sends a message to the new primary base station indicating aparticular sequence number that identifies the remaining packets offorward-link data queued at the old primary base station. The newprimary base station then sends a message to the FSD function requestingtransmission of those packets of forward-link data corresponding to theparticular sequence number. The FSD function then transmits thoserequested packets of forward-link data to the new primary base station,which queues the requested packets for over-the-air transmission to themobile unit. In this way, the present invention enables transmission ofall of the forward-link data to the mobile unit without having totransmit the remaining queued packets of forward-link data from the oldprimary base station to the new primary base station over the back haul,thereby providing an efficient mechanism for primary transfer inwireless communications systems that support forward-link datatransmissions only in simplex mode.

In one embodiment, the present invention is a wireless communicationsmethod, comprising the steps of (a) queuing packets of forward-link dataat a data distribution function of a wireless communications system,wherein each packet of forward-link data has a sequence number; (b)transmitting the packets of forward-link data from the data distributionfunction to only a current primary base station of the wirelesscommunications system; (c) queuing at the current primary base stationthe packets of forward-link data for transmission over an air interface;(d) determining at the current primary base station, before transmittingall of the packets of forward-link data queued at the current primarybase station, that the current primary base station is to become an oldprimary base station and a different base station of the wirelesscommunications system is to become a new primary base station; (e)transmitting from the old primary base station to the new primary basestation a message indicating a particular sequence number identifyingone or more remaining queued packets of forward-link data at the oldprimary base station; (f) transmitting from the new primary base stationto the data distribution function a request for one or more packets offorward-link data based on the particular sequence number; (g)transmitting from the data distribution function to the new primary basestation the requested one or more packets of forward-link data based onthe particular sequence number; and (h) queuing at the new primary basestation the requested one or more packets of forward-link data fortransmission over the air interface, thereby enabling transmission ofall of the forward-link data over the air interface without having totransmit the one or more remaining queued packets of forward-link datafrom the old primary base station to the new primary base station.

In another embodiment, the present invention is a wirelesscommunications system comprising a data distribution function incommunication with a current primary base station. The data distributionfunction is configured to (a) queue packets of forward-link data,wherein each packet of forward-link data has a sequence number; and (b)transmit the packets of forward-link data to only the current primarybase station. The current primary base station is configured to (c)queue the packets of forward-link data for transmission over an airinterface; (d) determine, before transmitting all of the packets offorward-link data queued at the current primary base station, that thecurrent primary base station is to become an old primary base stationand a different base station of the wireless communications system is tobecome a new primary base station; and (e) transmit to the new primarybase station a message indicating a particular sequence numberidentifying one or more remaining queued packets of forward-link data atthe old primary base station. The new primary base station is configuredto transmit to the data distribution function a request for one or morepackets of forward-link data based on the particular sequence number.The data distribution function is further configured to transmit to thenew primary base station the requested one or more packets offorward-link data based on the particular sequence number. The newprimary base station is further configured to queue the requested one ormore packets of forward-link data for transmission over the airinterface, thereby enabling transmission of all of the forward-link dataover the air interface without having to transmit the one or moreremaining queued packets of forward-link data from the old primary basestation to the new primary base station.

In another embodiment, the present invention is a wirelesscommunications method, comprising the steps of (a) queuing packets offorward-link data at a data distribution function of a wirelesscommunications system, wherein each packet of forward-link data has asequence number; (b) transmitting the packets of forward-link data fromthe data distribution function to only a current primary base station ofthe wireless communications system; (c) then receiving at the datadistribution function a request from a new primary base station of thewireless communications system for one or more of the packets offorward-link data based on a particular sequence number; and (d) thentransmitting from the data distribution function to the new primary basestation the one or more requested packets of forward-link data based onthe particular sequence number.

In another embodiment, the present invention is a wirelesscommunications method, comprising the steps of (a) receiving at acurrent primary base station of a wireless communications system packetsof forward-link data, wherein each packet of forward-link data has asequence number; (b) queuing at the current primary base station thepackets of forward-link data for transmission over an air interface; (c)determining at the current primary base station, before transmitting allof the packets of forward-link data queued at the current primary basestation, that the current primary base station is to become an oldprimary base station and a different base station of the wirelesscommunications system is to become a new primary base station; and (d)transmitting from the old primary base station to the new primary basestation a message indicating a particular sequence number identifyingone or more remaining queued packets of forward-link data at the oldprimary base station.

In another embodiment, the present invention is a wirelesscommunications method, comprising the steps of (a) receiving at a newprimary base station of a wireless communications system a messageindicating a particular sequence number identifying one or moreremaining queued packets of forward-link data at an old primary basestation of the wireless communications system; (b) transmitting from thenew primary base station to a data distribution function of the wirelesscommunications system a request for one or more packets of forward-linkdata based on the particular sequence number; (c) receiving at the newprimary base station the requested one or more packets of forward-linkdata; and (d) queuing at the new primary base station the requested oneor more packets of forward-link data for transmission over an airinterface.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present invention willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which:

FIG. 1 shows a block diagram of a conventional CDMA wirelesscommunications system;

FIG. 2 shows a functional block diagram of a portion of thecommunications system of FIG. 1 for a mobile unit operating in softhandoff with three base stations;

FIG. 3 shows a mobile unit in soft handoff with two base stations duringconventional reverse-link data transmissions from the mobile unit;

FIGS. 4A-C show representations of the protocol stacks for (A) a frameselection/distribution function, a radio link protocol function, and aninterworking function, (B) a base station, and (C) a mobile unit,respectively, for a wireless communications system in accordance withthe present invention;

FIGS. 5A-B show representations of forward-link data transfer scenariosfor mobiles in active and suspended states, respectively;

FIG. 6 shows a representation of a forward-link primary transferscenario;

FIG. 7 shows a representation of reverse-link scenarios;

FIG. 8 shows a representation of an example where the forward link is insimplex (one-way connection) and the reverse link is in two-way softhandoff; and

FIG. 9 shows a representation of an example where the forward link isnot active at all and the reverse link is in two-way soft handoff.

DETAILED DESCRIPTION

Communications systems of the present invention implement a wirelesspacket data approach that achieves low reactivation times when asupplemental channel is set up on a call to send a burst of packet data.According to this approach, when a mobile unit is otherwise operating insoft handoff, a forward supplemental channel (F-SCH) is not set up withmultiple soft handoff legs for forward-link transmissions, but ratheruses a single leg to perform the high-speed forward-link transmissionsof user data in simplex mode. For reverse-link soft handofftransmissions, the user data is carried by a reverse SCH (R-SCH) on eachof multiple legs to a frame selection/distribution (FSD) function. Thisapproach defines a single FSD function to handle both the signaling andthe SCH data packets and also defines packet-oriented semantics for itsconnection to the call legs. According to this approach, the powercontrol information, previously specified by CDMA wireless standardslike IS-95B/C to be carried on a forward-link signaling channel (i.e.,either an F-FCH or an F-DCCH), is instead carried on the common powercontrol channel (PCCH) that is shared with other mobiles.

The present approach addresses the problems described earlier related tousing the voice-oriented back haul architectures of prior-art IS-95wireless communications systems to support packet data service.Communications systems according to the present invention support softhandoff only on the reverse link and not on forward link. Note thatsofter handoff (i.e., between different sectors of the same cell site)is allowed on the forward link, since softer handoff is implementedindependently at individual base stations. Communications systems of thepresent invention use a connection-less back haul with a centralized FSDfunction, where the conventional RLP function in the forward directionis divided into two pieces and distributed between the FSD function andthe medium access control (MAC) function in the base station. Inparticular, the conventional RLP retransmission function is handled atthe FSD function, while the physical layer framing and resegmentation,CRC (error detection and correction), channel encoding, multiplexing ofmultiple streams, and any encryption functions, as well as schedulingand determination of transmission rate, are all handled at the basestation MAC function.

FIGS. 4A-C show representations of the protocol stacks for (A) an FSDfunction, an RLP function, and an IWF function, (B) a base station, and(C) a mobile unit, respectively, for a wireless communications system inaccordance with the present invention. A protocol stack provides arepresentation of the hierarchy of functions implemented at particularsystem component. FIGS. 4A-C show the following protocols:

T1 represents the protocol that controls the modulation/demodulation,encoding/decoding, and transmission/receipt of signals over the physicalconnection (e.g., a hardwired T1 link) between the FSD function and thebase station.

Phy represents the protocol that controls the modulation/demodulation,encoding/decoding, and transmission/receipt of signals over the physicalconnection (i.e., the air link) between the base station and the mobile.

BHL represents the back haul link, the protocol that directly controlsthe transmission of user information over the T1 link.

Similarly, MAC and MLC represent, respectively, the medium accesscontrol function and the MAC layer controller, which collectively anddirectly control the Phy protocol. In particular, the MAC functioncontrols the physical layer framing and resegmentation, while the MLCcontrols scheduling and MAC messaging.

ROLPC represents the reverse outer-loop power control function. Eachbase station generates quality-of-service (QoS) data based on thequality of reverse-link signals received from the mobile unit. The ROLPCfunction processes that QoS data to establish a set point that iscommunicated to and used by the base stations when they perform theRILPC (reverse inner-loop power control) function to generate the powercontrol bits for transmission to the mobile.

RLP represents the forward-link and reverse-link user messageretransmission function, which, according to some embodiments of thepresent invention, is still implemented by the FSD function. At themobile, RLP represents the forward-link and reverse-link user messageretransmission function as well as all of the other conventional RLPfunctions (e.g., segmentation and reassembly of user messages; also doneby the RLP function at the FSD function).

PPP represents the point-to-point protocol, which is the highest levelprotocol in both the FSD function and the mobile. At the mobile, PPPincludes the service provider's user interface that enables the user tosend and receive wireless transmissions to and from the mobile.

In preferred embodiments of the present invention, the protocol stack atthe mobile is identical to the mobile's protocol stack in prior-artIS-95 systems.

In communications systems of the present invention, the FSD functionforwards the forward-link packets to the primary base station that is inthe active set of the corresponding mobile. The forward-link RLPtransmit functionality is implemented in a distributed manner betweenthe base station (denoted BS/RLP) and the FSD function (denoted FS/RLP).The FS/RLP function divides incoming forward-link data into segments ofsize RLP_unit_size and assigns a unique RLP sequence number to each ofthe segments. The FS/RLP function then forwards the forward-link data tothe BS/RLP function along with this sequence number information.Physical layer framing is done by the BS/RLP function. This framing isdependent on the rate assigned by the base station MAC layer. Sincethere is no soft handoff on the forward link, resources for a data burstneed to be allocated at only one cell. This reduces the complexity anddelays involved in setting up supplemental channels in soft handoff.

The problems described in the background section are addressed in thepresent approach as follows:

1. FSD Function Server: Rather than establish an FSD function per call,which requires set up and release operations, a small number of FSDfunction servers is established. The FSD function initially selected fora call is not moved, even if primary transfer (i.e., changing thedesignation of primary cell from one base station to another) occurs.

2. Synchronization on Forward Link: Transmissions from a single leg onthe forward link avoids the necessity of synchronizing transmissionsfrom multiple cells. This eliminates the need for maintaining stricttiming constraints for transmissions between the FSD function and thebase stations, as is the case in the prior art. Delays that result fromestablishing forward-direction synchronization are avoided.

3. Synchronization on Reverse Link: Unlike voice, where time of arrivalis used for frame selection, RLP sequence numbers are used for packetdata applications. Since the data users can tolerate more jitter, thiseliminates the need for synchronization on the reverse link. Also, sincethe RLP function provides the equivalent functionality of frameselection by dropping duplicate messages, the frame selection functioncan be eliminated on the reverse link.

4. FSD function transmissions to the base stations do not need to besynchronized since there is no soft handoff on the forward link and alsosince data users, unlike voice users, can tolerate larger jitter.

5. Those mobiles that are not currently in the active data transmissionmode are kept in the suspended state, and the RLP state information,mobile capability, service option, and current active set informationfor the forward and reverse links are maintained. A sub-state called thesuspended (tracking) state is defined wherein the mobility of the useris tracked and the current active set information is updated. Thisminimizes the set-up delays when the user comes back into the activestate. These procedures eliminate the RLP synchronization overhead forfrequently active mobiles.

6. The segmentation functionality is separated from the RLP function.This eliminates the FS/RLP synchronization requirement imposed in theprior-art circuit-oriented architecture and the corresponding delays insetting up the supplemental channels.

To support the above architecture, communications systems of the presentinvention are provided with the following elements:

(a) Flow control between the base station and the FSD function toprevent the base station buffers from overflowing.

(b) Different priority queues used at the base station for (i)signaling, (ii) retransmission of old RLP data, and (iii) transmissionof new RLP data.

(c) Mechanisms that efficiently transfer control from one leg to anotherin case the mobile receives a much stronger pilot signal from a basestation that is not currently the primary.

(d) New ROLPC mechanisms since the prior-art ROLPC function is based onan architecture that maintains synchronism across different legs, souser messages from multiple call legs arrive simultaneously at the FSDfunction. In embodiments of the present invention, the base stationstamps the current GPS (global positioning system) time on each reverseframe received. The timestamps on frames received from multiple legs arethen used in deciding on frame erasures and updating the ROLPC setpoint.

(e) A new packet-mode FSD function that keeps a record for each of themobiles in either an active or suspended state with the followinginformation:

Mobile registration number—a number that uniquely identifies the mobile;

Addresses of RLP and IWF functions;

ROLPC state;

Addresses of the call legs; and

Active set—identification of those base stations currently operating insoft handoff with the mobile.

The following describes the architecture of a wireless communicationssystem, according to one embodiment of the present invention:

Packet Registration: At packet data registration (e.g., when the mobileuser turns on the mobile, or when the mobile enters a new base stationcoverage area while in the idle state), the IWF function selects aregistration number (reg_ID) that is unique within the IWF function.Associated with the reg_ID is the following information about theregistration: the IWF function, the FS/RLP server, last RLP sequencenumber used, and mobile capability (e.g., maximum transmission rate,etc.). At the IWF function, the reg_ID maps to an FS/RLP instance. An“instance” of a software functionality is a specific copy of thesoftware, which executes on a computer and is configured to provideservice. At the FSD function instance, the reg_ID is mapped to thecurrent active set, the current primary leg, base station addresses, theRLP function, and the ROLPC instance. At the base stations, reg_ID mapsto the address of the FSD function instance.

RLP function at FSD Function Server: When the FSD function is initiallyset up with a new reg_ID, it sets up an instance of the RLP function toserve the call. The RLP function provides the equivalent of frameselection functionality for data segments.

Frame Selection for Signaling Handled at Primary Cell: Signalingmessages (e.g., pilot strength measurement messages (PSMMs),supplemental channel requests messages (SCRMs)), except for RLP negativeacknowledgments (NAKs), received on the reverse link on all legs by theFSD function are echoed to the primary cell, as is done in the priorart. RLP NAKs are handled by the RLP function at the FSD function.

Active State (with DCCH): To minimize reactivation delay, the mobile cancome out of the suspended state and transmit on a dedicated controlchannel (DCCH) with minimal setup and delay, and remain on the DCCH fora period of time even if there is no data traffic.

Radio Link Protocol

The radio link protocol (RLP) function for the CDMA packet data serviceof the present invention satisfies the following conditions:

RLP framing, sequence numbering, and recovery do not depend on thephysical layer frame sizes and data rates on the air interface.

The RLP function requires no initialization when a mobile is reactivatedfrom the suspended state. The reg_ID is remembered during the suspendedstate and the RLP function is not aware of whether the mobile is activeor suspended. When the RLP function gets forward-link data for themobile, it sends the data to the primary leg. In addition the RLPfunction is always ready to receive packets from any of the active legs.

These conditions are achieved by dividing the RLP function in theforward direction into two pieces. The retransmission function ishandled at the FS/RLP function. The physical layer framing, CRC, channelencoding, multiplexing of multiple streams, and possibly encryptionfunctions, as well as scheduling and determination of transmission rate,are handled at the base station RLP function.

The RLP data unit size (RLP_unit_size) is chosen to be a small integernumber L of octets (i.e., 8-bit bytes). L=1 is desirable since a largerdata unit size can result in less efficient packing on the airinterface, but L=4 or 8 octets may be chosen to minimize sequence numberoverhead. Each RLP data unit is assigned a 20-bit sequence number. Thefull sequence number is used on the back haul link and when transmittingon the air interface at the higher data rates. At low data rates on theair interface, since the sequence numbers advance slowly, the lowerorder 16 bits of the sequence number are used. When there is ambiguity,retransmissions are used to carry the full sequence number.

An RLP segment comprises a number of RLP data units with consecutivesequence numbers. The RLP segment is identified by the sequence numberof the first data unit and the length (in number of in-sequence dataunits).

RLP control frames identify ranges of sequence numbers that are beingNAK-ed (or acknowledged (ACK-ed) if the RLP function is defined bystandards also provides positive acknowledgments). Retransmitted RLPdata segments are generated by the RLP function in response to NAKs. TheRLP function has a mechanism to catch loss of trailing new data. A pollis used to inform the BS/RLP function of the final sequence number sent,for which the BS/RLP function may provide a positive ACK to the FS/RLPfunction.

New data segments and data segments to be retransmitted are forwarded bythe FS/RLP function to the primary leg on the back haul link. In thereverse-link, data segments are received at the FS/RLP function frommultiple legs in the active set.

MAC: Resegmentation and Physical Layer Framing

The MAC function (i.e., BS/RLP) implemented at the base stationmaintains separate queues for retransmitted data (SAP 1) and new data(SAP 0) and gives priority to retransmitted segments. The base stationmay be able to check if it has duplicate retransmitted segments queuedup for transmission in SAP 1. In that case, the base station woulddiscard the later copy.

RLP data segments are transmitted over the air interface either on theSCH or on the DCCH, where the DCCH may be used to send signaling orsmall amounts of user data to the mobile. It is assumed that RLP datasegments are not sent simultaneously on the SCH and the DCCH. RLPcontrol frames (i.e., NAKs) and MAC and physical layer messages (e.g.pilot strength measurement messages (PSMMs), extended handoff directionmessage (EHDMs), supplemental channel assignment message (SCAMs) frombase station, supplemental channel request message (SCRMs) from mobile)are handled on the DCCH and are never multiplexed on a physical layerframe with user data. Messages sent on the DCCH may be transmitted atthe same time that RLP data segments are transmitted on the SCH.

For operation across multiple air interface rates, the physical layerframing structure allows multiplexing of new data (which is always insequence) and multiple retransmitted RLP segments. For new data, thesequence number identifying the first RLP data unit is used since therest of the data is in sequence. For retransmissions, an air interfaceframe format identifies a sequence number and an 8-bit length indicatorfor each retransmitted segment. Multiple retransmitted segments and upto one new data segment are accommodated in the air interface frameusing this format.

Encryption should be done in such a way that RLP sequencing istransparent to the cell. Possibilities include encryption at the cell orencryption above the RLP function. Encryption and compression above theRLP function can be done at the IWF function.

A 16-bit CRC is computed over the entire physical layer frame.

Back Haul Link Protocol

The back haul link (BHL) protocol provides framing of RLP segmentsbetween the FS/RLP function and the base station. RLP sequence numbersare used to identify the segments and only one in-sequence segment isincluded in one BHL frame. Depending on the maximum segment size on theBHL, the air interface physical layer frame may be segmented intomultiple BHL frames.

The RLP segment sequence number, message length, and address are theonly header fields required in the forward-link direction. Additionalheader fields are defined for the ROLPC function for use only in thereverse-link direction, including GPS time when used as a secondarysequence number, an erasure field, and a frame rate field.

The BHL protocol provides per-mobile flow control and recovery in theforward direction. A range of flow control options is possible: from asimple receiver ready/receiver not ready (RR/RNR) mechanism to afull-fledged leaky-bucket flow control. Tight flow controls are requiredif the system is to provide any quality-of-service (QoS) guarantees, butsince the RLP function can provide no back pressure, the flow control atthe base station is useful only to avoid congestion on the back haullink.

Since retransmitted segments have higher priority, retransmissions areprovided with a separate flow control window.

BHL recovery with a sequence number roll-back (Go Back N) mechanism isdefined. This provides recovery from buffer overflows as well as amechanism to switch to a new primary leg. If the RLP functionresynchronizes, it informs the base station to clear the buffers. Newdata in the new data buffer at the base station can be salvaged by usingthe roll-back to a common sequence number.

To minimize delays for reactivation and primary leg transfer, a separateaddress is provided for signaling on the BHL. In addition, the BHL atthe FSD function provides a base station relay function for:

Echoing of air interface reverse-link signaling messages from secondarylegs to the primary.

Routing of inter-base station messages for reverse-link burst admissioncontrol.

Routing of inter-base station messages for active set management.

Routing of primary transfer messages.

Depending on the implementation, the back haul facilities of the presentinvention may correspond to air links between the FSD function and thebase stations, rather than physical cables, such as T1 lines.

Reverse Outer Loop Power Control

Timing requirements on the back haul are simplified by implementing areverse outer loop power control (ROLPC) algorithm at the FSD function.The ROLPC function relies on frame rate and frame error indications fromall base stations in the active set. The frame rate is determined fromthe good frames received from any leg (correlated through the use of GPStime as the secondary sequence number). The primary cell is always awareof when a reverse link burst is active. An errored air interface frame(i.e., an erasure) is declared if an erasure is reported to the FSDfunction by the primary cell and there is no good frame for that GPStime from any other leg.

An outer loop power control scheme for bursty packet data could workwell for a data flow in a transaction that lasts several seconds. In thepresent approach, the ROLPC function is operated such that the set pointis remembered during the active state for the duration of a flow. Theset point expires if no reverse-link data is received for a timeoutperiod whose value is set, for example, to several seconds.

Normal Data Flow Operations on the Back Haul

Cell Reverse Link: If the air interface frame is received correctly, thebase station formats one or more BHL frames and sends them to the FSDfunction. The header includes frame rate, the RLP segment sequencenumber, and the GPS time as the secondary sequence number. If the airinterface frame is segmented into multiple BHL segments, the same GPSsecondary sequence number is used for each segment. A “more” bit may beused in the BHL header to indicate the existence of an additionalsegment. If the air interface frame is received in error at the primarycell, a BHL frame is transmitted to the FSD function with the headerindicating erasure and including the GPS time as the secondary sequencenumber.

FSD Function Reverse Link: All non-errored received segments are passedto the RLP function. The RLP function discards any duplicate octetsreceived. Frame rate, erasure, and the secondary sequence number (GPStime) are passed to the ROLPC function.

FSD Function Forward Link: The FSD function forwards RLP segments onlyto the primary base station, subject to flow control. If the currentprimary leg base station requests recovery with a roll-back sequencenumber, data beginning with the roll-back sequence number is forwardedagain.

Cell Forward Link: RLP segments corresponding to new data andretransmitted data that are received from the FSD function aretransferred to the new data and retransmitted data buffers,respectively. The RLP sequence numbers associated with the receivedsegments are remembered. For transmission on the air interface, one ormultiple segments along with segment sequence numbers are included inthe physical layer frame.

Operational Scenarios—Reactivation Soft Handoff and Primary Transfer

FIGS. 5A-B show representations of forward-link data transfer scenariosfor mobiles in active and suspended states, respectively, where timeflows from top to bottom in the figures. In the active state of FIG. 5A,data is forwarded by the FS/RLP function only to the primary basestation and data transfer can begin on the DCCH with no delay. Followingthe assignment of a supplemental channel and the sending of a quick(i.e., less than 20 msec taken to transmit the message over the airinterface) supplemental channel assignment message (SCAM) to inform themobile of the SCH assignment, the primary base station can begintransfer of user data on the supplemental channel. In the suspended(tracking) state of FIG. 5B, the FSD function is assumed to know theprimary leg to which it forwards new data. The primary base stationassigns a DCCH or a SCH as appropriate and sends the channel assignmentto the mobile (using a corresponding CAM or SCAM message), beforebeginning to transmit data on that assigned channel. Reactivation delayon the network is the time taken at the primary base station to make achannel assignment and send out the message followed by data on thededicated channel. The reactivation delay can be less than 30 ms.

When the reverse link is in soft handoff, the processing continues withthe scenario shown at the bottom of FIG. 5B. In particular, the mobiletransmits a pilot strength measurement message (PSMM), which causes theprimary to transmit a packet data handoff request (PDHOREQ) message tothe new base station being added to the reverse-link active set (i.e.,the new secondary base station). In FIG. 5B, the broken arrows signifythat, in some implementations, the messages are actually transmitted viathe FSD function. In other implementations, base stations may be able tocommunicate directly with one another without having to go through acentralized FSD function. In response, the new secondary base stationtransmits a packet data handoff acknowledgment (PDHOACK) message to theprimary base station, which then transmits an extended handoff directionmessage (EHDM) message back to the mobile. To minimize the reactivationdelay, data transfer on the forward link can begin before the newsecondary leg is added on the reverse link. To achieve a sufficientlyhigh probability of receiving the PSMM at the primary base station, themobile may need to use a high power and/or repeat the transmission ofthe PSMM.

FIG. 6 shows a representation of a forward-link primary transferscenario. Primary transfer begins when the mobile uses a PSMM message toreport to the primary leg that another (i.e., a secondary) leg has thestrongest pilot signal by some margin. The old primary sends a flowcontrol ON message to the FSD function (to prevent the FS/RLP functionfrom sending new data to the primary during the primary transferoperation) and sends a primary transfer message (PD_PRIM_XFER) to thenew primary. The PD_PRIM_XFER message contains the reg_ID and thereverse-link current active set for the mobile. The new primary thensends messages informing the FS/RLP function of its status as the newprimary (FS_NEW_PRIMARY) and instructing the FS/RLP function to turnflow control OFF (so any new data is now sent to the new primary by theFS/RLP function). In addition, the old primary sends a CAM message tothe mobile to instruct the mobile to transfer its operations into thesuspended (tracking) state, listening on the forward common controlchannel (F-CCCH) for transmissions from the new primary. The mobile willthen remain in the suspended (tracking) state, until new data isforwarded by the FS/RLP function to the new primary, at which time thenew primary will assign an appropriate channel, inform the mobile of thechannel assignment via a quick CAM/SCAM message, and begin data transferon that assigned channel.

If a forward burst is in progress when the old primary receives the PSMMmessage from the mobile, the old primary may continue the burst until itends or terminate the burst and have it restart at the new primary. Thisis accomplished as follows. The old primary includes the RLP segmentsequence number at the head of the new data queue (i.e., the roll-backsequence number) in the PD_PRIM_XFER message sent to the FS/RLPfunction. Data left in the retransmission queue, as well as any data inthe new data queue, at the old primary leg is assumed to be discarded.The retransmission queue should be small since retransmissions havepriority. The old primary informs the mobile that the current burst isterminated and instructs the mobile to transfer to the suspended(tracking) state, listening to the forward common control channel(F-CCCH) for the new primary. The new primary sends a new primarymessage (FS_NEW_PRIMARY) to the FSD function, indicating its address andthe roll-back sequence number, and turning flow control OFF. The FSDfunction sends all new data starting from the roll-back sequence numberto the new primary leg. The new primary, when it discovers the backlog,performs a quick CAM or quick SCAM to re-start the burst to the mobile.

Primary transfer involves handling a small number of messages at thebase station and on the back haul. The delays should be less than 20 ms.In addition, new data is forwarded to the new primary. The firstkilobyte of data can arrive in less than 10 ms. The primary transferdelay after the receipt of the PSMM can be achieved in the range of30-50 ms.

FIG. 7 shows a representation of reverse-link scenarios. A mobile in thesuspended (tracking) state makes an access on the random access channel(RACH) at the primary. The primary makes an immediate channel assignment(CAM) so that data can start flowing on the DCCH and the mobile can moveinto the active state. Notice that data transfer after reactivation canoccur prior to soft handoff set-up. The reactivation delay followingreceipt of the message on the RACH is less than 30 ms, including frametiming delays on the air interface.

If, based on the initial random access request, or later in the activestate, the mobile is required to have additional legs in soft handoff onthe reverse link, an inter-base station handoff request/grant scenariooccurs. For adding a leg, the primary sends a PDHOREQ proprietarymessage to the new secondary, including: the reg_ID, the FSD functionaddress, the ROLPC set point, mobile pseudo-noise (PN) code, and, if aburst is in progress, the burst end time and burst rate. The newsecondary base station can then join by simply sending the receivedreverse-link frame onto the BHL. The secondary base station acknowledgesthe handoff request by setting up a reverse-link inner loop powercontrol stream for the mobile and provides the information in thePDHOACK message to the primary, which then provides this information tothe mobile in the extended handoff direction message (EHDM). In thePDHOACK message, the secondary base station may require the terminationof a burst in progress. Initialization on the BHL between the secondarybase station and the FSD function is only needed to obtain futureupdates to the ROLPC set point; hence, there is no critical timingrequirement. When a leg drops from the call (when instructed by theprimary), it simply stops sending reverse frames to the FSD function. Asimple FSD function disconnect procedure is used, which is nottime-critical.

Finally, in FIG. 7, a burst acceptance scenario is shown. Therequest/grant scenario on the back haul is handled by the active setbase stations. The burst request/grant procedure involves processing offour messages at the base stations and transport of three messages onthe back haul. The total burst grant delay after the receipt of the SCRMto the transmission of the SCAM can be made less than 50 ms.

Power Control

Prior-art IS-95 standards assume that the active sets (i.e., those basestations currently communicating with a particular mobile unit) for bothforward and reverse links are the same. That is, traffic and controlchannels are set up symmetrically. This implies that a dedicated trafficchannel on the reverse link will have an associated dedicated powercontrol channel in the forward link to control the mobile units transmitpower level.

In the prior-art cdma2000 standard, the reverse-link transmit power iscontrolled by the forward-link power control sub-channel if it ispresent. During the active state, the power control sub-channel ismultiplexed (i.e., punctured) either on the forward dedicated controlchannel (F-DCCH) or on the forward fundamental channel (F-FCH). Thisrequires a symmetric active set to be maintained by the forward link andthe reverse link, as shown in FIG. 3. In other words, if the reverselink is in soft handoff, then the forward link has to be in the softhandoff even if it is not otherwise needed.

The presence of high-speed data users presents unique challenges insystem design due to the asymmetric nature of traffic. For efficientoperation of packet mode services, it is desirable to have asymmetricsupport for the forward and reverse active sets. The prior-art IS-95standards do not provide power control support for this mode ofoperation.

The present approach addresses the issue of power control feedback whenthe forward and reverse links have different active sets. For example,the forward link may be in one-way connection (i.e., simplex mode), ormay not be connected at all, while the reverse link may be in two-wayconnection (soft handoff).

In order to serve non-symmetric active set operation, the presentapproach involves a decoupling of the power control sub-channel fromboth the F-DCCH and the F-FCH and instead using the common power controlchannel (PCCH) to control the reverse-link power when the mobile is inthe active state. As defined in the prior-art cdma2000 standard, theforward-link common power control channel (F-PCCH) is a set of powercontrol sub-channels time multiplexed on a single physical channel.Under the cdma2000 standard, each power control sub-channel on theF-PCCH controls the reverse-link enhanced access channel (R-EACH) poweror the reverse-link common control channel (R-CCCH) power for adifferent mobile serviced by the base station transmitting the F-PCCH.An R-EACH is used by a mobile in either the dormant or suspended stateto request assignment of a dedicated traffic channel. Dormant andsuspended states are similar in that the mobile has no dedicated airinterface channels assigned. In the suspended state, some informationabout the mobile user data session is maintained in the base station,whereas, in the dormant state, none is. An R-CCCH may be used by amobile in the dormant state to send a relatively short burst of data,without having to request and be assigned a dedicated traffic channel.

The prior-art cdma2000 standard does not allow the F-PCCH to control thereverse-link dedicated control channel (R-DCCH) power or thereverse-link traffic channel (R-FCH or R-SCH) power. The presentapproach removes this restriction so that the F-PCCH can control thereverse-link transmit power while a mobile is in the active state. Thisapproach provides power control at the mobile unit when the forward linkand the reverse link have different active sets.

FIG. 8 shows a representation of an example where the forward link is insimplex (one-way connection) and the reverse link is in two-way softhandoff. On the forward link, base station A has an F-FCH or an F-DCCHactive. On the reverse link, the mobile unit is in soft handoff withbase stations A and B. The mobile's transmit power is controlled by bothbase stations via the common power control channels F-PCCHa and F-PCCHb,respectively. There is no power control sub-channel punctured on theF-FCH or on the F-DCCH transmitted by base station A. Alternatively, thepower control sub-channel from base station A could be punctured on theF-FCH or F-DCCH, while base station B transmits its power controlsub-channel via F-PCCHb. To extend the example of FIG. 8 further, basestation A can have a supplemental channel (F-SCH) active on the forwardlink in addition to either the F-DCCH or F-FCH. In any case, under thisapproach, there is no need to establish F-DCCH or F-FCH from both basestations in order to provide power control.

FIG. 9 shows a representation of an example where the forward link isnot active at all and the reverse link is in two-way soft handoff. Onthe forward link, there is no F-FCH or F-DCCH or F-SCH active. On thereverse link, the mobile unit is in soft handoff with both base stationsA and B using an R-DCCH, R-FCH, and/or R-SCH. The mobile's transmitpower is controlled by both base stations via F-PCCHa and F-PCCHb,respectively.

At its most basic, the techniques described herein eliminate nearly alldelay on the back haul interface between a base station and a FSD/RLPfunction when reactivating a packet data user from a state where theuser has been inactive for some time, and a high-speed air interfacechannel needs to be re-established for use by the user. Prior art usescircuit-oriented techniques and procedures on the back haul interface,in which there are many interactions between the base station and theFSD/RLP function when activating or reactivating users.

In CDMA systems according to the present invention, the network-basedRLP function is divided into two parts: one that may execute at acentral place in the network and one that executes in the base station.(Alternatively, both parts may execute in the base station.) Thecentrally located part (i.e., the part that may execute remotely fromthe base station) performs the functions of retransmission control. Thepart located in the base station performs the function of sending theuser messages over the air. These functions include those of physicallayer framing and re-segmentation, error detection and correction of airinterface messages, channel encoding, multiplexing of multiple streams,encryption, determination of over-the-air transmission rates, andscheduling of over-the-air transmission. This separation enables theuser messages to be forwarded immediately to the base station with thebest opportunity to provide good communications with the mobile unit. Notime synchronous coordination is required between the base station andthe (possibly) remote part of RLP function, and no air interface limitsare imposed on the amount of data that can be sent to the base stationfor a given call at a given point in time.

The centrally located part of the network-based RLP function sends userdata from the network to one and only one call leg, namely the one withthe best signal to the mobile user. That call leg determines how andwhen to transfer the user messages to the mobile unit over the airinterface.

The determination of which base station has the best signal to themobile user is performed by the base station, and the knowledge of this“primary” base station is passed to the centrally located part of thenetwork-based RLP function. This concept may be referred to as “primarytransfer for high-speed packet data services.”

Two queues are kept in the primary base station to handle user messagesthat need to be sent over the air to the mobile user. One queue, calledthe “new data” queue, keeps new user messages, namely, messages thathave not already been sent to the user. The other queue, called the“retransmission” queue, keeps user messages that have already beentransmitted to the mobile unit, but which have not been received, orwhich have been received in error by the mobile unit. Priority forover-the-air transmission is given to the user messages on theretransmission queue.

An over-the-air transmission can contain multiple user message segmentsfrom the retransmit queue, plus one message segment from the new dataqueue. This capability makes optimal use of the air interface capacity.The messages from the retransmission queue are packed first into the airinterface frame, and have an RLP sequence number, plus a length (inunits of bytes allocated to a unit of increment of the RLP sequencenumber). The user message segment from the new data queue contains anRLP sequence number, and continues to the end of the air interfaceframe.

When a primary transfer occurs, the current primary leg uses flowcontrol on the back haul to prevent the remote part of RLP function fromsending data to a call leg that is in the process of changing its statusfrom being primary to being a secondary call leg. The current primarypasses to the new primary the RLP sequence number representing all newuser data still remaining in the new data queue. When the primarytransfer operation is completed, the new primary call leg informs theremote part of RLP function of its address and removes the back haulflow control. In this process, the new primary also informs the remoteRLP function of the sequence number with which to begin sending new usermessages. Hence, the remote RLP function in effect sends to the newprimary the user data that had not yet been transmitted by the oldprimary. This capability avoids having the old primary leg send itsunsent data to the new primary, thereby saving transport time andutilization. (Such cell-to-cell transport would be required if bothparts of the network-based RLP function executed in the base station.Either the primary transfer capability would not be part of theimplementation, and the solution would require, in general, thatcell-to-cell user data transport occur, or the primary transfercapability would be designed into the implementation, but additionalinteractions between cells and a frame selection/distribution functionwould be required to make the system work.)

Both signaling and user message transmission over the air interface inthe forward direction (to the mobile unit) are performed in simplexmode, from a single call leg. Alternatively, signaling and user messagetransfer in the reverse direction (to the base station and FSD function)occur in general using multiple call legs in soft handoff. The powercontrol subchannel punctured into a forward-link channel to control themobile reverse-link transmission power needs to be decoupled from thededicated forward-link air interface channels, as described above.

The FSD function, together with the remote part of the network-based RLPfunction form a server application that is assigned to the high-speedpacket data call when the call is first established. This serverinstance is not changed, regardless of whether the mobile user remainsinactive for long periods of time, or whether primary transfer occurs.This server is always ready to accept data from the network todistribute to the primary leg for transmission to the mobile user, andis always ready to receive user messages from any of the soft handofflegs that are part of the call. After a first initialization, no time isrequired to initialize with the mobile unit, even when the user isreactivated after a long idle time duration.

Reverse-link user messages from the mobile unit can arrive at theFSD/RLP server (or function) from multiple legs at times that differwidely from one another. Any user message correctly received at any legis accepted by the FSD function, because the RLP function discardsduplicate messages.

The reverse-link user messages sent from the call legs have both an RLPsequence number and a portion of the value of the GPS time embeddedwithin them. The RLP sequence number is used by the RLP function todetect missing or duplicate messages. The GPS time is used by the FSDfunction to associate one or more back haul information packets with thetime of transmission of the information over the air interface. Themaximum size of the back haul packet transmissions is in generaldifferent from the number of user information elements (i.e., bytes)that can fit in a 20-msec air interface frame. Hence, one air interfaceframe worth of user data may occupy more than one packet on the backhaul facility when it is transferred to the FSD/RLP function. The airinterface frame rate and quality indicators are used at the FSD functionto calculate a set point value, the so-called ROLPC value, which isreturned tall call legs, so they can control the power transmitted bythe mobile unit.

To properly calculate the ROLPC set point value, the calculation has todetermine when all legs receive the same air interface frame in error.For circuit mode services, information on the traffic-bearing airinterface channel is always present, but in a high-speed packet dataservice, user message transmissions are bursty. The primary call legalways knows when a supplemental channel is assigned, so it can generatea back haul frame with an erasure indicator (i.e., an air interfaceframe was expected, but was not received, or was received in error),plus a GPS time stamp. If no other leg delivers over the back haul acorrect air interface message with the same GPS time, the ROLPCcalculation function at the FSD function uses an erasure for thecalculation.

The protocol used on the back haul between the base station and theFSD/RLP function has separate addresses for user message transfer andfor inter-base station communications, and for communication of mobileunit signaling. If the FSD function receives a back haul packet havingthe address used for mobile unit signaling communications, the messageis forwarded to the primary base station. (The primary base station isresponsible for interpreting and responding to the signaling messagesfrom the mobile unit. These messages are received over the air interfaceby all legs, but need to be echoed to the primary leg in case thereception at the primary leg of the air interface transmission from themobile is in error.) If the FSD function receives a back haul packethaving the address used for inter-base station communications, itforwards the message to the call leg, or legs, specified in the messagebody. If the FSD function receives a back haul message having theaddress of user message transfer, it passes the message to itsassociated RLP function.

If there is an air interface channel assigned to the mobile unit forsignaling (i.e., either an F-FCH, or an F-DCCH), data forwarded to theprimary leg from the FSD/RLP function causes a control message to besent to the mobile unit, containing the code point of the F-SCH that isto carry the user message. Because no coordination is needed with theprimary leg before the FSD/RLP function sends the user message, thereactivation time for this forward-link transmission is minimized. Whenno user message exchanges are going on, the mobile continues to reportits pilot strength measurements to the primary, in case another basestation becomes the one with the strongest signal at the location of themobile unit. Primary transfer occurs, if necessary, and the reactivationtime to send new data to the mobile user is again minimized.

If the mobile user has data to send in the reverse direction, and theuser currently has a signaling air interface channel assigned on thereverse link to the call legs, the user can either immediately beginsending the data using the R-FCH or R-DCCH (whichever is assigned), orit can send a signaling message requesting a higher rate air interfacechannel to be assigned. The mobile unit can continue to use thesignaling channel to transfer user data until the higher speed airinterface channel assignment is received by it. These mechanics minimizereactivation delay for reverse-link exchanges when the mobile has anassigned signaling air interface channel.

When the mobile unit is not active on any air interface channel, and theprimary leg receives user messages from the FSD/RLP function, theprimary leg uses a forward-link common signaling air interface channelto assign a F-SCH to the mobile. Transmissions to the mobile user ensue.Because there is no negotiation interactions between the primary leg andthe FSD/RLP function, and no negotiation interactions among the calllegs (transmissions in the forward direction are simplex, from theprimary leg only), the reactivation time is minimized.

When the mobile unit is not active on any air interface channel, and themobile user has data to send to the network, it sends a signalingmessage on a reverse common signaling channel, requesting the assignmentof reverse air interface channels for its data transmission. Once theseare assigned, the mobile can begin its data transmission, as discussedabove. No synchronization is required to be performed with the FSDfunction, and no initializations are required. Hence, the back haulcommunications add no delay to the user reactivation time.

Although the present invention has been described in the context ofIS-95 CDMA wireless systems, it will be understood that the presentinvention may be able to be implemented in CDMA wireless systemsconforming to standards other than the IS-95 family of standards, e.g.,the European Telecommunications Standard Institute (ETSI) family ofstandards. Similarly, the present invention may be able to beimplemented in wireless systems other than CDMA systems such as FDMA(frequency division multiple access) or TDMA (time division multipleaccess) systems.

It will be further understood that various changes in the details,materials, and arrangements of the parts which have been described andillustrated in order to explain the nature of this invention may be madeby those skilled in the art without departing from the scope of theinvention as expressed in the following claims.

What is claimed is:
 1. A wireless communications method, comprising thesteps of: (a) queuing packets of forward-link data at a datadistribution function of a wireless communications system, wherein eachpacket of forward-link data has a sequence number; (b) transmitting thepackets of forward-link data from the data distribution function to onlya current primary base station of the wireless communications system;(c) queuing at the current primary base station the packets offorward-link data for transmission over an air interface; (d)determining at the current primary base station, before transmitting allof the packets of forward-link data queued at the current primary basestation, that the current primary base station is to become an oldprimary base station and a different base station of the wirelesscommunications system is to become a new primary base station; (e)transmitting from the old primary base station to the new primary basestation a message indicating a particular sequence number identifyingone or more remaining queued packets of forward-link data at the oldprimary base station, wherein packets associated with one or moresequence numbers prior to the particular sequence number define a firstportion of the data for transmission over the air interface by the oldprimary base station and packets associated with the particular sequencenumber define a second portion of the data; (f) transmitting from thenew primary base station to the data distribution function a request forone or more packets of forward-link data based on the particularsequence number; (g) transmitting from the data distribution function tothe new primary base station the requested one or more packets offorward-link data based on the particular sequence number; and (h)queuing at the new primary base station the requested one or morepackets of forward-link data for transmission of the second portion overthe air interface, thereby enabling transmission of all of theforward-link data over the air interface without having to transmit theone or more remaining queued packets of forward-link data from the oldprimary base station to the new primary base station, and wherein thefirst portion of the data and the second portion of the data are nottransmitted over the air interface in synchronism.
 2. The invention ofclaim 1, wherein the wireless communications system is an IS-95 CDMAsystem and the data distribution function is part of a frameselection/distribution (FSD)/radio link protocol (RLP) function.
 3. Theinvention of claim 1, wherein, at different times, each primary basestation transmits forward-link data in simplex mode, when correspondingreverse-link operations are in soft handoff.
 4. The invention of claim1, wherein each primary base station has a new data queue forforward-link data that has not been previously transmitted over the airinterface and a retransmission queue for forward-link data that has beenpreviously transmitted over the air interface.
 5. The invention of claim4, wherein the retransmission queue has a higher transmission prioritylevel than the new data queue.
 6. The invention of claim 4, wherein atleast one forward-link transmission over the air interface from aprimary base station comprises one or more user message segments fromthe retransmission queue and a user message segment from the new dataqueue.
 7. The invention of claim 1, wherein the message indicating theparticular sequence number is transmitted from the old primary basestation to the new primary base station via the data distributionfunction.
 8. A wireless communications system comprising a datadistribution function in communication with a current primary basestation, wherein: the data distribution function is configured to: (a)queue packets of forward-link data, wherein each packet of forward-linkdata has a sequence number; and (b) transmit the packets of forward-linkdata to only the current primary base station; the current primary basestation is configured to: (c) queue the packets of forward-link data fortransmission over an air interface; (d) determine, before transmittingall of the packets of forward-link data queued at the current primarybase station, that the current primary base station is to become an oldprimary base station and a different base station of the wirelesscommunications system is to become a new primary base station; and (e)transmit to the new primary base station a message indicating aparticular sequence number identifying one or more remaining queuedpackets of forward-link data at the old primary base station, whereinpackets associated with one or more sequence numbers prior to theparticular sequence number define a first portion of the data fortransmission over the air interface by the old primary base station andpackets associated with the particular sequence number define a secondportion of the data; the new primary base station is configured totransmit to the data distribution function a request for one or morepackets of forward-link data based on the particular sequence number;the data distribution function is further configured to transmit to thenew primary base station the requested one or more packets offorward-link data based on the particular sequence number; and the newprimary base station is further configured to queue the requested one ormore packets of forward-link data for transmission of the second portionover the air interface, thereby enabling transmission of all of theforward-link data over the air interface without having to transmit theone or more remaining queued packets of forward-link data from the oldprimary base station to the new primary base station, and wherein thefirst portion of the data and the second portion of the data are nottransmitted over the air interface in synchronism.
 9. The invention ofclaim 8, wherein the wireless communications system is an IS-95 CDMAsystem and the data distribution function is part of a frameselection/distribution (FSD)/radio link protocol (RLP) function.
 10. Theinvention of claim 8, wherein, at different times, each primary basestation transmits forward-link data in simplex mode, when correspondingreverse-link operations are in soft handoff.
 11. The invention of claim8, wherein each primary base station has a new data queue forforward-link data that has not been previously transmitted over the airinterface and a retransmission queue for forward-link data that has beenpreviously transmitted over the air interface.
 12. The invention ofclaim 11, wherein the retransmission queue has a higher transmissionpriority level than the new data queue.
 13. The invention of claim 11,wherein at least one forward-link transmission over the air interfacefrom a primary base station comprises one or more user message segmentsfrom the retransmission queue and a user message segment from the newdata queue.
 14. The invention of claim 8, wherein the message indicatingthe particular sequence number is transmitted from the old primary basestation to the new primary base station via the data distributionfunction.
 15. A wireless communications method, comprising the steps of:(a) queuing packets of forward-link data at a data distribution functionof a wireless communications system, wherein each packet of forward-linkdata has a sequence number; (b) transmitting the packets of forward-linkdata from the data distribution function to only a current primary basestation of the wireless communications system; (c) then receiving at thedata distribution function a request from a new primary base station ofthe wireless communications system for one or more of the packets offorward-link data based on a particular sequence number, wherein packetsassociated with one or more sequence numbers prior to the particularsequence number define a first portion of the data for transmission overthe air interface by the current primary base station and packetsassociated with the particular sequence number define a second portionof the data; and (d) then transmitting from the data distributionfunction to the new primary base station the one or more requestedpackets of forward-link data of the second portion based on theparticular sequence number, wherein the first portion of the data andthe second portion of the data are not transmitted over the airinterface in synchronism.
 16. The invention of claim 15, wherein thewireless communications system is an IS-95 CDMA system and the datadistribution function is part of a frame selection/distribution(FSD)/radio link protocol (RLP) function.
 17. A wireless communicationsmethod, comprising the steps of: (a) receiving at a current primary basestation of a wireless communications system packets of forward-linkdata, wherein each packet of forward-link data has a sequence number;(b) queuing at the current primary base station the packets offorward-link data for transmission over an air interface; (c)determining at the current primary base station, before transmitting allof the packets of forward-link data queued at the current primary basestation, that the current primary base station is to become an oldprimary base station and a different base station of the wirelesscommunications system is to become a new primary base station; and (d)transmitting from the old primary base station to the new primary basestation a message indicating a particular sequence number identifyingone or more remaining queued packets of forward-link data at the oldprimary base station, wherein packets associated with one or moresequence numbers prior to the particular sequence number define a firstportion of the data for transmission over the air interface by the oldprimary base station and packets associated with the particular sequencenumber define a second portion of the data, and wherein the firstportion of the data and the second portion of the data are nottransmitted over the air interface in synchronism.
 18. The invention ofclaim 17, wherein the wireless communications system is an IS-95 CDMAsystem.
 19. The invention of claim 17, wherein the current primary basestation transmits forward-link data over the air interface in simplexmode, when corresponding reverse-link operations are in soft handoff.20. The invention of claim 17, wherein the current primary base stationhas a new data queue for forward-link data that has not been previouslytransmitted over the air interface and a retransmission queue forforward-link data that has been previously transmitted over the airinterface.
 21. The invention of claim 20, wherein the retransmissionqueue has a higher transmission priority level than the new data queue.22. The invention of claim 20, wherein at least one forward-linktransmission over the air interface from the current primary basestation comprises one or more user message segments from theretransmission queue and a user message segment from the new data queue.23. The invention of claim 17, wherein the message indicating theparticular sequence number is transmitted from the old primary basestation to the new primary base station via a frame distributionfunction of the wireless communications system.
 24. A wirelesscommunications method, comprising the steps of: (a) receiving at a newprimary base station of a wireless communications system a messageindicating a particular sequence number identifying one or moreremaining queued packets of forward-link data at an old primary basestation of the wireless communications system; (b) transmitting from thenew primary base station to a data distribution function of the wirelesscommunications system a request for one or more packets of forward-linkdata based on the particular sequence number, wherein packets associatedwith one or more sequence numbers prior to the particular sequencenumber define a first portion of the data for transmission over the airinterface by the old primary base station and packets associated withthe particular sequence number define a second portion of the data; (c)receiving at the new primary base station the requested one or morepackets of forward-link data; and (d) queuing at the new primary basestation the requested one or more packets of forward-link data fortransmission of the second portion over an air interface, and whereinthe first portion of the data and the second portion of the data are nottransmitted over the air interface in synchronism.
 25. The invention ofclaim 24, wherein the wireless communications system is an IS-95 CDMAsystem and the data distribution function is part of a frameselection/distribution (FSD)/radio link protocol (RLP) function.
 26. Theinvention of claim 24, wherein the new primary base station transmitsforward-link data over the air interface in simplex mode, whencorresponding reverse-link operations are in soft handoff.
 27. Theinvention of claim 24, wherein the new primary base station has a newdata queue for forward-link data that has not been previouslytransmitted over the air interface and a retransmission queue forforward-link data that has been previously transmitted over the airinterface.
 28. The invention of claim 27, wherein the retransmissionqueue has a higher transmission priority level than the new data queue.29. The invention of claim 27, wherein at least one forward-linktransmission over the air interface from the new primary base stationcomprises one or more user message segments from the retransmissionqueue and a user message segment from the new data queue.
 30. Theinvention of claim 24, wherein the message indicating the particularsequence number is transmitted from the old primary base station to thenew primary base station via a frame distribution function of thewireless communications system.